Membrane foulant

See also Colloidal silica gels Colloidal graphite, 12 795 Colloidal liquids, 7 294-295 Colloidal materials, as membrane foulants, 21 664... 

Protegrin derivatives, 18 260 Protegrins, 18 260-261 properties of, 18 261 Protein. See also Proteins extraction of, 26 474 in cereal grains, 26 275-276 Proteinaceous materials, as membrane foulants, 21 664 Protein adsorption, 12 136-137 Protein affinity libraries, 12 516-517 Protein-based chiral phases, 6 89-90 Protein-based microarrays, 16 382 Protein biosynthesis, 20 450... 

Table 2.5 Commonly used cleaning chemicals for the removal of membrane foulants...

An additional benefit of the activated carbon was the scouring of the membrane surface to remove membrane foulants. Not only was the exponential decay in flux arrested, the flux was restored to its inital value as shown in Figure 43. 

Beer clarihcation by microhltration requires a hne balance between the retention of large particles and the transmission of soluble macromolecules such as carbohydrates, proteins, as well as flavor and color compounds, which contribute to beer quality. Proteins and carbohydrates are known membrane foulants, but they are also essential for beer quality. Sufficient... 

K. Nakano, S. Ogawa, T. Oku, T. Sata, R. Izuo and K. Ideue, Treating method of waste solution from galvanizing process, Jpn. Pat. No. 1123641 H.C. Heller and V Markovac, Identification of a membrane foulant in the electrodialysis recovery of nickel, Anal. Chem., 1983, 55, 551. 

Maartens A., Swart P., Jacobs E.P. (1998), Humic membrane foulants in natural brown water characterisation and removal, Desalination, 115, 215-227. 

Speth T.F., Summers R.S., Gusses A.M. (1996), Evaluating membrane foulants from conventionally-treated drinking waters. Natural Organic Matter Workshop, Poitiers, France, September 96, 44. 

Valladares Linares, R., Yangali-Quintanilla, V, Li, Z. Amy, G. (2012) NOM andTEP fouling of a forward osmosis (FO) membrane foulant identification and cleaning. Journal of Membrane Science, 421-422, 217-224. 

The success of a reverse osmosis process hinges direcdy on the pretreatment of the feed stream. If typical process streams, without pretreatment to remove partially some of the constituents Hsted, were contacted with membranes, membrane life and performance would be unacceptable. There is no single pretreatment for all types of foulants. Pretreatment methods range from pH control, adsorption (qv), to filtration (qv), depending on the chemistry of the particular foulant. Some of the pretreatment methods for each type of foulant are as foUow (43—45) ... 

Flux response to concentration, cross flow or shear rate, pressure, and temperature should be determined for the allowable plant excursions. Fouling must be quantified and cleaning procedures proven. The final design flux should reflect long-range variables such as feed-composition changes, reduction of membrane performance, long-term compaction, new foulants, and viscosity shifts. 

Pretreatment For most membrane applications, particularly for RO and NF, pretreatment of the feed is essential. If pretreatment is inadequate, success will be transient. For most applications, pretreatment is location specific. Well water is easier to treat than surface water and that is particularly true for sea wells. A reducing (anaerobic) environment is preferred. If heavy metals are present in the feed even in small amounts, they may catalyze membrane degradation. If surface sources are treated, chlorination followed by thorough dechlorination is required for high-performance membranes [Riley in Baker et al., op. cit., p. 5-29]. It is normal to adjust pH and add antisealants to prevent deposition of carbonates and siillates on the membrane. Iron can be a major problem, and equipment selection to avoid iron contamination is required. Freshly precipitated iron oxide fouls membranes and reqiiires an expensive cleaning procedure to remove. Humic acid is another foulant, and if it is present, conventional flocculation and filtration are normally used to remove it. The same treatment is appropriate for other colloidal materials. Ultrafiltration or microfiltration are excellent pretreatments, but in general they are... 

Fouling Fouling affec ts MF as it affects all membrane processes. One difference is that the fouling effect caused by deposition of a foulant in the pores or on the surface of the membrane can be confounded by a rearrangement or compression of the sohds cake which may form on the membrane surface. Also, the high, open space found in tortuous-pore membranes makes them slower to foiil and harder to clean. 

A critical consideration with UF technology is the problem of fouling. Foulants interfere with UF by reducing product rates- sometimes drastically-and altering membrane selectivity. The story of a successful UF application is in many respects the story of how fouling was successfully controlled. Fouling must be considered at every step of UF process development in order to achieve success. 

When we talk about this subject, the term foulant or foulant layer comes to the forefront. Foulant, or fouling layer, are general terms for deposits on or in the membrane that adversely affect filtration. The term "fouling" is often used indiscriminately in reference to any phenomenon that results in reduced product rates. "Fouling" in this casual sense can involve several distinct phenomena. These phenomena can be desirable or undesirable, reversible or irreversible. Different technical terms apply to each of these possibilities. 

Cake layer formation builds on the membrane surface and extends outward into the feed channel. The constituents of the foulant layer may be smaller than the pores of the membrane. A gel layer can result from denaturation of some proteins. Internal pore fouling occurs inside the membrane. The size of the pore is reduced and pore flow is constricted. Internal pore fouling is usually difficult to clean. 

Polyphosphinocarboxylic acid. Products based on this chemical tend to be suitable for brackish waters up to say 10,000 to 15,000 ppm TDS and where high sulfates are present (200 to 300 ppm as S04). A feature of this type of chemical is not only its ability to deal effectively with carbonate and sulfate scaling in higher TDS waters but also the fact that it has dispersant properties of benefit in physically moving potential foulants away from the membrane surface. 

The type of membrane cleaning required depends on both the type and degree of fouling experienced, but typically it is either organic (bacterial slimes, natural organics, or process foulants and nutrients) or inorganic (silica, carbonate, sulfate, or phosphate deposits). 

A measurement of silt, colloids, bacteria, and other rapid foulants of RO membranes. The SDI test is used to determine the SDI of water and thus its suitability for an RO process. SDI of above 5.0 indicates the water is unacceptable. Ideally the water should have an SDI of below 1.0. 

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